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1.
Real and imaganiry parts of complex dielectric constant of dilute solutions of DNA in 10?3M NaCl with molecular weight ranging from 0.4 × 106 to 4 × 106 were measured at frequencies from 0.2 Hz to 30 kHz. Dielectric increments Δε were obtained from Cole-Cole plots and relaxation times τD from the loss maximum frequency. The τD of all samples agrees well with twice of the maximum viscoelastic relexation time in the Zimm theory, indicating that the low-frequency dielectric relaxiation should be ascribed to be the rotation of DNA. The rms dipole moment, which was obtained from Δε, agree well with that calculated from the counterion fluctuation theory. The dielectric increment was found to be greatly depressed in MgCl2, which is resonably interpreted in terms of a strong binding of Mg++ ions with DNA.  相似文献   

2.
The complex dielectric constant of collagen in aqueous solutions (polymer concentration, Cp = 0.02–0.2%) was measured at 10°C in the frequency range from 3 Hz to 30 kHz. The loss peak for Cp = 0.02% is located at 90 Hz and the dielectric relaxation time τD is estimated to be 1.8 ± 0.3 msec. The τD agrees well with the rotational relaxation time estimated from the reduced viscosity, and the relaxation is ascribed to the end-over-end rotation of the molecule. The Cp dependence of τD and the dielectric increment Δε are interpreted in terms of the aggregation of molecules. The dipole moment of a molecule, obtained from Δε at Cp = 0.02% and pH 6.5, is (5.2 ± 0.2) × 104D, which is explained by the asymmetrical distribution of the ionized side chains of the molecule.  相似文献   

3.
M Sakamoto  R Hayakawa  Y Wada 《Biopolymers》1979,18(11):2769-2782
As a continuation of previous papers [Biopolymers (1976) 15 , 879; (1978) 17 , 1508], the low-frequency dielectric relaxation of DNA solutions was studied with a four-electrode cell and the simultaneous two-frequency measurement. Below a critical concentration, the dielectric relaxation time agrees with the rotational relaxation time estimated from the reduced viscosity and is almost independent of DNA concentration Cp, and the dielectric increment is proportional to Cp. The critical concentration is approximately 0.02% of DNA for molecular weight Mr 2 × 106 and 0.2% for Mr 4.5 × 105 in 1 mM NaCl. Dielectric relaxations are compared for samples before and after deproteinization, and the protein contamination is found to have a minor effect on the dipole moment of DNA. The effect of a mixed solvent of water and ethanol on the dielectric relaxation of DNA is well interpreted in terms of changes in viscosity and the dielectric constant of the solvent, assuming that the relaxation arises from rotation of the molecule with a quasi-permanent dipole due to counterion fluctuation.  相似文献   

4.
Dielectric relaxation of DNA in aqueous solutions.   总被引:1,自引:0,他引:1  
Using a four-electrode cell and a new electronic system for direct detection of the frequency differences specturm of solution impedance, the complex dielectric constant of calf thymus DNA (Mr = 4 × 106) in aqueous NaCl at 10°C is measured at frequencies ranging from 0.2 Hz to 30 kHz. The DNA concentrations are Cp = 0.01% and 0.05%, and the NaCl concentrations are varied from Cs = 10?4 M to 10?3 M. A single relaxation regions is found in this frequency range, the relaxation frequency being 10 Hz at Cp = 0.01% and Cs = 10?3 M. At Cp = 0.05% it is evidenced that the DNA chains have appreciable intermolecular interactions. The dielectric relaxaton time τd at Cp = 0.01% agrees well with the rotational relaxation time estimated from the reduced visocisty on the assumption that the DNA is not representable as a rigid rod but a coiled chain. It is concluded that the dielectric relaxiatioinis ascribed to the rotation of the molecule. Observed values of dielectric increment and other experimental findings are reasonably explained by assuming that the dipole moment of DNA results from the slow counterion fluctuation which has a longer relaxation time than τd.  相似文献   

5.
K L Wun  W Prins 《Biopolymers》1975,14(1):111-117
Quasi-elastic light scattering as measured by intensity fluctuation (self-beat) spectroscopy in the time domain can be profitably used to follow both the translational diffusion D and the dominant internal flexing mode τint of DNA and its complexes with various histones in aqueous salt solutions. Without histones, DNA is found to have D = 1.6 × 10?8 cm2/sec and τint ? 5 × 10?4 sec in 0.8 M NaCl, 2 M urea at 20°C. Total histone as well as fraction F2A induce supercoiling (D = 2.6 × 10?8 cm2/sec, τint ? 2.8 × 10?4 sec) whereas fraction F1 induces uncoiling (D = 1.0 × 10?8 cm2/sec, τint ? 9.4 × 10?4 sec). Upon increasing the salt concentration to 1.5 M the DNA–histone complex dissociates (D = 1.8 × 10?8 cm2/sec). Upon decreasing the salt concentration to far below 0.8 M, the DNA–histone complex eventually precipitates as a chromatin gel.  相似文献   

6.
B Lubas  T Wilczok 《Biopolymers》1971,10(8):1267-1276
The molecular mobility of calf thymus DNA molecules in solution has been discussed in terms of correlation time τ calculated from measurements of longitudinal T1 and transverse T2 magnetic relaxation times. The influence of DNA concentration and ionic strength of the solution upon freedom of movement of DNA molecules was studied for native and denatured DNA and also during thermal helix-coil transition. The dependence of τ values on temperature was carried out by comparing the values of correlation times τtat given temperature with the correlation time τ20 at 20°C. The molecular rotation of DNA at 20°C and at higher ionic strength at 0.15 and 1.0.M NaCl is described by τ values of the order of 1.0–1.2 × 10?8 and was reduced slightly with increase of temperature below the helix-coil transition. The molecular rotation of DNA in 0.02MNaCl was lower at 20°C as compared to DNA in solvents with higher NaCl concentrations and increases rapidly with increase of temperature in the range 20–60°C. The values of correlation time are characterized by fast increase at temperatures above the spectrophotometrically determined beginning of melting curve. The beginning of this increase is observed at about 65, 80, and 85°C for DNA in 0.02, 0.15, and 1.0MNaCl, respectively. Values of correlation time for denatured DNA are in all cases about 1.1–1.4 times that for native DNA. The obtained results are discussed in terms of conformation of DNA molecules in solution as well as in terms of water dipole binding in DNA hydration shells.  相似文献   

7.
31P-Nmr relaxation parameters (spin-lattice relaxation time, linewidth, and nuclear Overhauser effect) were obtained at three different frequencies for poly(U) and a well-defined (145 ± 3 base-pair) fragment of DNA in solution. Data sets for the two samples were analyzed by theories which included relaxation by the mechanisms of 31P chemical shift anisotropy as well as by 1H-31P dipole–dipole interaction. Neither data set could be satisfactorily described by a single correlation time. A model of a rigid rotor most nearly fits the data for the DNA molecule. Parameters obtained from the least-square fit indicate (1) that the DNA undergoes anisotropic reorientation with a correlation time τ0 = 6.5 × 10?7 sec for the end-to-end motion, (2) the ratio of diffusion constants D/D is 91, and (3) that the linewidth is due to chemical shift dispersion to the extent of 0.5 ppm. Some deviations of the calculated from the observed values suggested that significant torsional and bending motions may also take place for this DNA. Another model which contains isotropic motion but with a broad distribution of correlation times was required to fit the data for poly(U). A log ? χ2 distribution function of correlation times [Scheafer, J. (1973) Macromolecules 6 , 881–888] described well the motion of poly(U) with the average correlation time τ = 3.3 × 10?9 sec and a distribution parameter p = 14.  相似文献   

8.
In solutions containing DNA and cations of more than one type, the competitive interactions of these cations with DNA can be modeled as an ion exchange process that can be described quantitatively by means of the theoretical approach reported in this paper. Under conditions of experimental interest the radial distribution function of each type of counterion is calculated from the results of canonical Monte Carlo (MC) simulations using the primitive model for DNA (having a helical charge distribution) and for the electrolyte ions. These ions consist of monovalent coions, monovalent counterions intended to represent Na+, and counterions of a second type designated Mz+, having variable size and charge (z ≥ 1). The competitive association of these counterions with DNA is described in terms of D, a parameter analogous to an ion exchange equilibrium quotient. Values of D are calculated from the results of our MC simulations and compared with corresponding predictions of the Poisson–Boltzmann (PB) cell model and with results inferred from analyses of previously published nmr measurements. Over typical experimental concentration ranges (0.02M < [Na+] < 0.20M, 0.001 < [Mz+] < 0.160M), DMC and DPB both are predicted to be relatively independent of the bulk ion concentrations. For various specifications of the size and charge of the competing cation (Mz+), DMC and DPB exhibit similar trends, although the MC simulations consistently predict that the cations bearing a higher charge density than that of Na+ are somewhat stronger competitors than indicated by the PB calculations. For monovalent and divalent competitors of varying radii, theoretical predictions of D are compared with values obtained by fitting nmr measurements. If the hard-sphere radii specified in the simulations are the (hydrated) ionic radii determined from conductance measurements, then the MC predictions and the corresponding nmr results are in reasonable agreement for various monovalent competitors and for a divalent polyamine, but not for Ca2+ and Mg2+.  相似文献   

9.
Dirk Stigter 《Biopolymers》1998,46(7):503-516
We have studied electrostatic properties of DNA with a discrete charge model consisting of a cylindrical dielectric core with a radius of 8 Å and a dielectric constant Di = 4, surrounded by two helical strings of phosphate point charges at 10 Å from the axis, immersed in an aqueous medium with dielectric constant Dw = 78.54. Eliminating the dielectric core makes potentials in the phosphate surface less negative by about 0.5 kT/e. Salt effects are evaluated for the model without a dielectric core, using the shielded Coulomb potential. Smearing the phosphate charges increases their potential by about 2.5 kT/e, due mostly to the self-potential of the smeared charge. Potentials in the center of the minor and major grooves vary less than 0.02 kT/e along their helical path. The potential in the center of the minor groove is from 1.0 to 1.7 kT/e, more negative than in the center of the major groove, depending on dielectric core and salt concentration. So multivalent cations and also larger cationic ligands, such as some antibiotics, are likely to adsorb in the minor groove, in agreement with earlier computations by A. and B. Pullman. Dielectric effects on the surface potential and the local potential variations are found to be relatively small. Bending of DNA is studied by placing a multivalent cation, MZ+, in the center of the minor or major groove, curving DNA around it for a certain length, and calculating the free energy difference between the bent and the straight configuration. Boltzmann averaged bending angles, 〈β〉, are found to be maximal in 0.03M monovalent salt, for a length of about 50 or 25 Å of curved DNA when an MZ+ ion is adsorbed in the minor or the major groove, respectively. When the dielectric constant of water is used throughout the calculation, we find maximal bends of 〈β〉 = 11° for M2+ and 〈β〉 = 16° for M3+ in the minor groove, 〈β〉 = 13° for M3+ in the major groove. The absence of bends in DNA adsorbed to mica in the presence of Mg salts supports the role of Mg2+ in “ion bridging” between DNA and mica. The treatment of the effective dielectric constant between two points outside a dielectric cylinder in water is appended. © 1998 John Wiley & Sons, Inc. Biopoly 46: 503–516, 1998  相似文献   

10.
23Na-NMR investigations of counterion exchange reactions of helical DNA   总被引:2,自引:0,他引:2  
Changes in Δν½, the nmr linewidth of 23Na, have been determined during titrations of helical DNA with polyamines (divalent putrescine and trivalent spermidine) and with inorganic cations (Mg2+ and Co(NH3)). In each case additions of a multivalent cation (Mz+) to a solution containing NaDNA and NaCl cause decreases in Δν½, which is a population-weighted average of contributions from nuclei in bound and free environments. Thus, the binding of Mz+ to DNA displaces sodium ions from regions where the quadrupolar relaxation of 23Na is relatively efficient. At a given extent of titration, the binding of a polyamine produces a smaller decrease in Δν½ than does the binding of an inorganic ion of the same valence. The concentration dependence of Δν½ during the course of a titration can be interpreted most simply as a two-state ion-exchange reaction by assuming that the binding of Mz does not alter RB, the average relaxation rate of sodium nuclei that remain bound. On the basis of this assumption, the initial linear portions of titration curves can be analyzed to determine upper bounds for r°, the number of sodium ions bound per DNA phosphate in the absence of any competing counterion. Analyzing the titration curves for the four multivalent competitors leads to a range of upper-bound estimates for r°: 0.5–0.8. The differences in these estimates could indicate that polyamines displace fewer sodium ions from DNA than do their smaller inorganic counterparts. Alternatively, the range in upper-bound estimates for r° could also reflect specific differences in the effects of the various multivalent cations on RB, if this relaxation rate does change during titration.  相似文献   

11.
The preparation and melting of a 16 base-pair duplex DNA linked on both ends by C12H24 (dodecyl) chains is described. Absorbance vs temperature curves (optical melting curves) were measured for the dodecyl-linked molecule and the same duplex molecule linked on the ends instead by T4 loops. Optical melting curves of both molecules were measured in 25, 55, and 85 mM Na+ and revealed, regardless of [Na +], the duplex linked by dodecyl loops is more stable by at least 6°C than the same duplex linked by T4 loops. Experimental curves in each salt environment were analyzed in terms of the two-state and multistate theoretical models. In the two-state, or van't Hoff analysis, the melting transition is assumed to occur in an all-or-none manner. Thus, the only possible states accessible to the molecule throughout the melting transition are the completely intact duplex and the completely melted duplex or minicircle. In the multistate analysis no assumptions regarding the melting transition are required and the statistical occurrence of every possible partially melted state of the duplex is explicitly considered. Results of the analysis revealed the melting transitions of both the dodecyl-linked molecule and the dumbbell with T4 end loops are essentially two state in 25 and 55 mM Na+. In contrast, significant deviations from two-state behavior were observed in 85 m MNa+. From our previously published melting data of DNA dumbbells with Tn end loops where n = 2, 3, 4, 6, 8, 10, 14 [T. M. Paner, M. Amaratunga, and A. S. Benight, (1992) Biopolymers, Vol. 32, pp. 881–892] and the dumbbell with T4 end loops of this study, a plot of d(Tm)/d ln [Na+] was constructed. Extrapolation of this data to n = 1 intersects with the value of d (Tm)/d ln [Na+] obtained for the alkyl-linked dumbbell, suggesting the salt-dependent stability of the alkyl-linked molecule behaves as though the duplex of this molecule were linked by end loops comprised of a single T residue. © 1993 John Wiley & Sons, Inc.  相似文献   

12.
Intercalation of cationic dyes in the DNA double helix: introductory theory   总被引:1,自引:0,他引:1  
The effect of salt on the intercalation of acridine dyes and DNA is rather well explained by the Gouy-Chapman double-layer theory as applied to a cylinder model of the DNA–dye complex. The free energy of transfer of a dye ion from the bulk solution to the complex is divided into several parts, one of which, ΔF0, accounts for the short-range, nonelectrostatic interactions. The assumption that ΔF0 should not depend on the amount of dye in the complex leads to an internal dielectric constant of the cylinder of about Di = 7. The scatter in ΔF0 values, as calculated from individual experimental points, is of order 0.5 kT per dye ion. This scatter is large enough to mask possible effects of heterogeneity in DNA sequences. The calculations are made for a long cylinder with radius 10 Å, with the DNA phosphate charges smeared uniformly at the surface, a uniform spacing of dye charges at the cylinder axis, and a length of b = 3.37 Å per base pair. Each intercalated dye ion also adds a length b to the total length of the cylinder. The salt-dependent part of the electric free energy of intercalation, ΔF1, is tabulated for complexes with r = 0–0.24 dye ions per DNA phosphate in 0.002–0.2M monovalent salt and dye solutions.  相似文献   

13.
Dielectric dispersion curves for the helix-11 form of poly-L-proline in aqueous solution have been determined for various pH in the acid range of zwitterion formation. The results could be excellently described by means of a Cole-Cole dispersion function involving the three parameters Δ?0 (total dielectric increment), τr (effective rotational relaxation time) and h (characterizing the width of the dispersion region). The quantities τr, and h were found to be clearly independent of pH and added inert electrolyte. An analysis of the data permits an evaluation of the dipole moments and leads to the conclusion that the molecule cannot be considered to be a completely stretched rigid rod but must be more or less bent. Addition of formic acid slightly below pH 4 caused a distinct broadening of the experimental curves which could be quantitatively interpreted by a second dielectric relaxation process due to orientation of zwitterions by means of fast proton transfer.  相似文献   

14.
《Chronobiology international》2013,30(7):1335-1347
Circadian clocks continue to oscillate in constant conditions with their own period (τ) and entrain to a cyclic environment by adjusting their intrinsic period to that of the zeitgeber. When circadian clocks are released from entrained to constant conditions, the τ of their initial free-run often depends on the nature of the prior zeitgeber. These postentrainment effects on period (τ-aftereffects) have predominantly been reported for animals but, so far, not fungi. The authors therefore investigated τ aftereffects in the classic circadian model system Neurospora crassa. The standard laboratory strain frq+, the short-period mutant frq1, and the long-period mutant frq7 were entrained to 11 different photoperiods in a 24-h day (2–22?h) and to zeitgebers with six different T (16–26?h), and then released to constant darkness. τ-Aftereffects in response to different photoperiods correlated weakly with prior photoperiod in frq+ and were unsystematic in both period mutant strains. Strength and direction of the τ-aftereffect in zeitgeber cycles with different T depended on their length and on the strain, showing a negative correlation with zeitgeber length in frq+ and positive correlations in frq1 and frq7. It has been proposed that τ-aftereffects are based on interactions of oscillators within a cellular network. The present findings in Neurospora, which grows as a syncytium, suggest that τ-aftereffects also exist in circadian systems based on multioscillatory networks organized at the molecular level. (Author correspondence: )  相似文献   

15.
At 0°C, when Na+ was the only cation present in the incubation medium, increasing the Na+ concentration from 3 to 10 mM enhanced the affinity of [3H]l-[2-(di-phenylmethoxy)ethyl]-4-(3-phenyl-2-propenyl)piperazine ([3H]GBR 12783) for the specific binding site present in rat striatal membranes without affecting the 5max. For higher Na+ concentrations, specific binding values plateaued and then slightly decreased at 130 mM Na+. In a 10 mM Na+ medium, the KD and the Bmax were, respectively, 0.23 nM and 12.9 pmol/mg of protein. In the presence of 0.4 nM [3H]GBR 12783, the half-maximal specific binding occurred at 5 mM Na+. A similar Na+ dependence was observed at 20°C. Scatchard plots indicated that K+, Ca2+, Mg2+, and Tris+ acted like competitive inhibitors of the specific binding of [3H]GBR 12783. The inhibitory potency of various cations (K+, Ca2+, Mg2+, Tris+, Li+ and choline) was enhanced when the Na+ concentration was decreased from 130 to 10 mM. In a 10 mM Na+ medium, the rank order of inhibitory potency was Ca2+ (0.13 mM) > Mg2+ > Tris+ > K+ (15 mM). The requirement for Na+ was rather specific, because none of the other cations acted as a substitute for Na+. No anionic requirement was found: Cl-, Br-, and F- were equipotent. These results suggest that low Na+ concentrations are required for maximal binding; higher Na+ concentrations protect the specific binding site against the inhibitory effect of other cations.  相似文献   

16.
Quasielastic light scattering is used to study the effect of ionic strength on the dynamic behaviour of DNA. In a first approach the spectrum of scattered light is analyzed in terms of a single relaxation process. The large difference between the observed behaviour and that expected according to a pure diffusional process reflects the contribution associated with internal modes, which increases with decreasing ionic strength. Such behaviour is better analyzed in terms of a double relaxation process by using two relaxation times, the reciprocals of which are equal to DK2 and DK2 + τi?1 (K), respectively, where τi (K) is an average value describing the set of modes observed at a given K value. Relative intensity and relaxation times, which are the more accurate parameters, were used to interpret the results. The observed increase of the relative contribution of internal modes with decreasing ionic strength is actually a relative decrease of the diffusional contribution induced by a corresponding increase of the radius of gyration RG. On the other hand, the reciprocal τi?1 (K) of the relaxation time is a linear function of K2 in the analyzed KRG range and is insensitive to ionic strength between 10?2M and 1M. These results, when discussed according to Rouse's model, lead to define for each value of τi?1 (K) a corresponding mean-squared equilibrium length 〈μ〉 which is found to be a linear function of K?2.  相似文献   

17.
F G Walz  B Terenna  D Rolince 《Biopolymers》1975,14(4):825-837
Spectrophotometric binding studies were undertaken on the interaction of neutral red with native and heat-denatured, sonicated, calf thymus DNA in a 0.2M ionic strength buffer containing Tris–sodium acetate–potassium chloride at 25°C. The pKA of neutral red was found to be 6.81. At pH 5 the binding of protonated neutral red was complicated even at low concentration ratios of dye to DNA. In the pH range 7.5–8.5 the tight binding process could be studied and it was found that both protonated and free base species of neutral red significantly bind with DNA having association constants (in terms of polynucleotide phosphate) of 5.99 × 103 M?1 and 0.136 × 103 M?1, respectively, for native DNA and 7.48 × 103 M?1 and 0.938 × 103 M?1, respectively, for denatured DNA. The pKA value of the neutral red–DNA complexes were 8.46 for native DNA and 7.72 for denatured DNA. These results are discussed in terms of possible binding mechanisms.  相似文献   

18.
Glucose, galactose, and mannose in H2O and D2O were ionized by an atmospheric pressure chemical ionization (APCI) method. Isotope effects on fragmentation patterns of the monosaccharides were examined by deuterium replacement of the -OH groups to distinguish the isomers with a single mass spectrometer. The most abundant ions were the [M+H2O]+ and [MD5+D+D2O]+ for using H2O and D2O as solvent and eluent, respectively. Major fragment ions were the [M−OH]+ and [M−OH−H2O]+ in H2O, while those in D2O were the [MD5+D−D2O]+ and [MD5+D−2D2O]+. The differences in the product ions generated in H2O and D2O were due to enhancement of the strength of hydrogen bonding by the deuterium replacement. Variations of the ion intensity ratios of the [M−OH]+/[M−OH−H2O]+ and [MD5−OD]+/[MD5−OD−D2O]+ with the fragmentor voltage showed different trends depending on the kind of monosaccharides. By comparing the ion intensity ratios of the [M+H2O]+/M+, [MD5+D+D2O]+/[MD5+D]+, [M−OH]+/[M−OH−H2O]+, and [MD5+D−D2O]+/[MD5+D−2D2O]+, it was possible to distinguish the isomers of monosaccharides.  相似文献   

19.
Alcaligenes xylosoxydans subsp. xylosoxydans A-6 (Alcaligenes A-6) produced N-acyl-D-aspartate amidohydrolase (D-AAase) in the presence of N-acetyl-D-aspartate as an inducer. The enzyme was purified to homogeneity. The enzyme had a molecular mass of 56 kDa and was shown by sodium dodecyl sulfate (SDS)–polyacrylamide gel electrophoresis (PAGE) to be a monomer. The isoelectric point was 4.8. The enzyme had maximal activity at pH 7.5 to 8.0 and 50°C, and was stable at pH 8.0 and up to 45°C. N-Formyl (Km=12.5 mM), N-acetyl (Km=2.52 mM), N-propionyl (Km=0.194 mM), N-butyryl (Km=0.033 mM), and N-glycyl (Km =1.11 mM) derivatives of D-aspartate were hydrolyzed, but N-carbobenzoyl-D-aspartate, N-acetyl-L-aspartate, and N-acetyl-D-glutamate were not substrates. The enzyme was inhibited by both divalent cations (Hg2+, Ni2+, Cu2+) and thiol reagents (N-ethylmaleimide, iodoacetic acid, dithiothreitol, and p-chloromercuribenzoic acid). The N-terminal amino acid sequence and amino acid composition were analyzed.  相似文献   

20.
Movements of ions are considered to be governed by the electroneutrality rule. Therefore, a cation moving across the cell membrane into the cell either passively or actively should move together with its counterion, an anion, in equal amounts of charge or in exchange for another cation inside the cell. This means that the net influx of the cation in question should be affected by the permeability of its counterion and/or another cation inside the cell. To examine osmotic and ionic regulation in Chara cells, cell fragments of Chara having a lower osmotic pressure than normal (L-cell fragments) were prepared. The L-cell fragments were individually put into various dilute electrolyte solutions and their osmotic potentials were measured with a turgor balance. Concentrations of K+, Na+, Ca2+, Mg2+, Cl?, NO?3. and SO2?4. in the external electrolyte solutions in which L-cells had been incubated were also analysed by ion chromatography. The results showed that in 0.5 mM KCL + 0.1 mM CaCl2 solution, Chara L-cell fragments absorbed K+ and Cl? to maintain electroneutrality and then regained their osmotic potential very rapidly. When the anion was Cl, the cation absorbed at the highest rate was K+ On the other hand, when the cation was K, the anion absorbed at the highest rate was Cl, Other ions Ca2+, SO2?4 and NO?3 showed much less permeability than K+ and Cl ?for the Chara plasma membrane. The conclusion from these findings was that due to the constraint of electroneutral transport, the uptake rate of a salt into L-cells is limited by the permeability of the least permeable ion.  相似文献   

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